The present invention relates to a headphone with high audio-signal conversion efficiency and sound quality.
The widespread of portable music players has recently made the market of headphones active.
The headphone is divided into several types, such as, an overhead type equipped with a headband and resting on the user's head and an inner-ear type to be fit in the antihelix of a user's ear.
A housing, the main body of a headphone, requires to be light weight because the headphone is rested on the user's head or fit in the antihelix of a user's ear. Thus, generally, the housing is produced by resin injection molding or light-metal processing. A resin material is used, especially, for low cost production.
Installed in the housing is a speaker unit that converts audio signals into sounds and outputs the sounds.
It is known that several problems occur when the installed speaker unit is in direct contact with a resin-made housing.
A problem is, for example, a big difference in sound quality depending on the types of resin material, the shape of housing, etc. even if headphones are equipped with the identical speaker units.
Another problem is lowered audio-signal conversion efficiency due to the attenuated energy of vibration in the housing without given off outwardly when transferred from the speaker unit. This is because resin exhibits low stiffness so that it can absorb the energy of vibration well, thus causing a high internal loss in transfer of vibration.
A technique to solve such problems is disclosed in Japanese Un-Examined Patent Publication No. 2009-60207 (referred to as a document 1, hereinafter) applied by the applicant of the present patent application.
Disclosed in the document 1 a headphone equipped with a speaker unit that is fixed to a fixing ring that is fixed to a housing so that the speaker unit is not in direct contact with the housing, the fixing ring having a higher specific gravity than the housing.
Especially, shown in (b) of FIG. 1 and also FIG. 3 of the document 1 are headphones each equipped with a speaker unit that is supported by a fixing ring at the rear and side faces of the speaker unit, the fixing ring having a higher specific gravity than a housing.
The headphones disclosed in the document 1 thus exhibit high audio-signal conversion efficiency and sound quality achieved with the fixing ring that receives the reaction of a diaphragm of the speaker unit in the opposite direction (the rear side) of a sound-emitting side (the front side) to which the diaphragm moves while vibrating.
Nevertheless, the headphones still have room for improvement in audio-signal conversion efficiency and sound quality because the fixing ring cannot receive the reaction of the diaphragm to the front side that is caused by the movement of the diaphragm to the rear side while vibrating.